I am making a cake for a friend who does not want a fondant cake but would like the look of the pearl dust on buttercream. I have heard that pearl dust only works with fondant so does anyone know of a way I can get that same shimmer effect or will the pearl dust work?

Incorporating the dust into the b/c doesn't work.

If you use a crusting b/c, you can dust gently for a sparkly effect.

Everything there is to know about the various dusts:
(Including hints and tips on usage.)

http://www.cakecentral.com/cake-decorating-ftopict-54059.html

HTH

P.S. Everything you need to know to make, decorate and assemble tiered/stacked/layer cakes:

http://www.cakecentral.com/cake-decorating-ftopict-605188.html

Above super thread has popular CC recipes for crusting American buttercreams (b/c), several types of fondant and doctored cake mix (WASC and other flavor variations) - and so much more! (One of the mores is several methods of smoothing crusted b/c so that it looks like fondant.)